Venting and flaring are common practices throughout the oil industry that involve the intentional release of natural gas into the atmosphere or burning of natural gas at oilfield sites. Oil wells typically produce both oil and natural gas. Many times, the quantity of associated natural gas produced is too little for its recovery to be economically viable. In other cases, the infrastructure is not available for transportation of the natural gas. The release of natural gas into the atmosphere creates a safety hazard, as it is capable of generating explosive mixtures with air. Furthermore, natural gas is primarily composed of methane, which is a strong greenhouse gas. Owing to the aforementioned concerns, flaring is routinely performed to convert natural gas into carbon dioxide and water vapor. Although carbon dioxide is a less potent greenhouse gas than methane, it is still a concern for its anthropogenic greenhouse effect on global warming.
In offshore oilfield operations, and many remote onshore locations, it is desirable for the oilrig or platform to be self-sufficient to the furthest extent possible and capable of generating its own electricity. This is typically achieved through the use of diesel or gas-powered generators.
Beyond the concerns with venting/flaring of natural gas and the provision of electricity to remote oilrigs or platforms, there exist numerous problems that are common to offshore and some onshore oilfield operations that are particularly related to flow assurance issues. As referred to herein, “flow assurance” refers to ensuring the successful and economic flow of reservoir fluids from the reservoir to a wellhead and surface equipment. Reservoir fluids produced in many fields, and particularly in offshore oil wells, undergo a significant temperature drop during transit through the well and associated well string employed for conveying the reservoir fluids out of the well. In particular, during production from deep sea reservoirs, reservoir fluids can undergo a significant temperature decline upon entering a segment of well string that spans from the reservoir to the wellhead. In the case of offshore wells, the temperature contrast is significantly more pronounced at the seafloor because of the surrounding cold seawater.
It is common for reservoir fluids to be a mixture of crude oil, natural gas (i.e. methane), and water. Dissolved solids also commonly exist within the reservoir fluid, including asphaltenes and paraffins. Methane hydrate, also termed methane clathrate, is chemically described as CH4.5.75 H2O and can typically form at ocean depths greater than 300 m and temperatures around 2° C. when methane is present with water. The aforementioned temperature drop can generate solid methane hydrates, along with inducing precipitation of asphaltenes and paraffin wax from the reservoir fluids. The presence of solid methane hydrates, asphaltenes, and/or paraffin wax within the reservoir fluids can create restrictions and impact flow assurance in the well string, among other issues. In particular, upon precipitation, the asphaltenes, and paraffins (as well as formed methane hydrate) may be deposited on the inner surface of the oil well and the well string, thus inhibiting flow of the reservoir fluids from the oil well.
The presence of solid methane hydrates, asphaltenes, and/or paraffin wax can lead to the partial or full blockage of a well. Partial blockage of the well generates an elevated pressure drop that impacts well productivity. Costly intervention techniques are generally employed to eliminate the blockages and recover well productivity. The intervention techniques typically involve shutting-down the well to treat the subsea section that has been blocked.
The presence of methane hydrate in an oil well is of further concern because fluid flow can become destabilized. Methane hydrate exists in the solid phase under certain temperature/pressure conditions within the undersea reservoirs. As the solid methane hydrates are transported with the reservoir fluids to the surface, the reservoir fluids become warmer and the methane hydrates generally undergo sublimation. In this manner, gas pockets of methane are formed within the well and/or well string that leads from the seabed to the water surface, potentially destabilizing flow of the reservoir fluids.
Aside from flow assurance issues resulting from the presence of solid methane hydrates, asphaltenes, and/or paraffin wax, reservoir pressure is also a factor in flow assurance. The natural pressure within an oil reservoir can be used to lift the reservoir fluids to the surface. When reservoir pressure is not sufficient or the pressure has declined, however, artificial lift methods are available. Different artificial lift systems include, for example: electric submersible pumps (ESPs), hydraulic pumps, rod pumps, and gas lift. ESPs are placed downhole and utilize an electric motor to generate fluid displacement and thus move oil up the well. Hydraulic piston pumps are also placed downhole, but use hydraulic fluid pumped down from the surface to drive a lifting mechanism. Rod pumps operate from the surface and utilize vertical movement of a rod to induce lifting of the oil. Gas lift involves the injection of gas into the reservoir to push oil to the surface. Each of the aforementioned artificial lift methods require energy for operation, which is typically in the form of electricity.
The aforementioned artificial lift systems generally require electricity to operate. Some artificial lift systems, ESPs in particular, require electricity to be conveyed downhole. For instance, present methods for providing electricity to the ESPs involve the use of cables that tether the ESP to a power supply located above the well. The depth at which an ESP may have to be located in a well can lead to a significant loss of electricity via resistance from the long cable. Thus, electrical conveyance efficiency can be a concern for some ESP systems, especially for ESP units that must be located deep within a well.
Accordingly, it is desirable to provide oilfield electricity and heat generation systems and methods that address the present difficulties with supplying electricity for artificial lift systems and other on-site operations. It is also desirable to provide oilfield electricity and heat generation systems and methods that provide thermal energy to address flow assurance issues and other thermal energy needs. It is also desirable to provide alternatives to flaring/venting of natural gas, especially for oilrigs or platforms that are in remote and/or offshore locations. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.